The purpose of this project is to elucidate the mechanisms regulating estrogen production in primate pregnancy. The following approaches are being used: (1) identification and quantitation of the different circulating estrogen precursors; (2) determination of factors controlling availability of such precursors; (3) examination of the effects of variations in precursor availability on estrogen production; (4) determinations of placental biosynthetic capacity for estrogen synthesis. The studies also provide an evaluation of the baboon as a model of human pregnancy.